Late Shoreline Fluctuations of Manix, : Paleoclimate Implications

Marith C. Reheis, David M. Miller, and John P. McGeehin Regional setting of

Lake Thompson Why study the Mojave?

¾Presently occupies a transition zone between areas dominated by westerly Pacific winter moisture and southerly monsoon summer moisture ¾Terrestrial climate proxies may record changing influence of these moisture sources D-O cycles H events ? PDO ENSO NAM, PNA…..? fed Lake Manix between about 500 ka and 25 ka; occasionally, river diverted to

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543 m (in blue), controlled by s ≤ Late P highstands were threshold near Afton Canyon and internal sill to Coyote Lake 14 C dating sites (Anodonta shells) Each dot typically represents multiple dates / sites Calibrated using Fairbanks et al. conversion Late lake phases

Lake 8 (MIS 3): Mostly shallow- water sand and gravel preserved

Lake 7 (MIS 6-4?): Mostly deeper-water green mud interbedded with sand at line -co

Tufa-coated clasts commonly mark lake transgressions in gravelly sediment Upper Dunn Wash— fluvio-lacustrine deposits

Tufa-coat lines Buried soil

36.8 ka

40.1 ka Upper Lake 8 Dunn Wash sections Lake 7 Other selected sections east west Coyote Lake dating sites

543 m barrier beach

35535 36690 31700 46800

33640 35220

27030

Post-Manix (25 ka) river and lake deposits SE Lake Coyote: stratigraphy & interpretation

M08SM-940 Many rapid fluctuations indicated by ostracode-hash “death beds”

Shell bed 36.7 cal ka

M07SM-2448

Shell bed 33.6 cal ka

Buried soil vaguely laminated gypsic sand

fine and med sand, rippled with 30.1 14Ckyr mud drapes in upper 4 cm

hard mud and vfi sand, ripple laminated

14 loose med sand, well sorted, 38.4 Ckyr laminated hard blocky mud; floating sand grains; one shell layer; one thin sand in middle. Soil? loose medium sand, faintly laminated

mud with lenses and v. thin beds of sand, some rippled SE Coyote Lake—hand dug pit plus outcrop

¾Thin sedimentary packages ¾Small-scale stratigraphy reveals complex record ¾Three main lake phases separated by exposure and soil formation Hiatus / soil fm. Provisional lake-level curve Other events affecting lake level

Spilling into/ out of Coyote lake Coyote sill altitude

Afton Canyon cut

Diversion to Harper L? Comparison to other Comparison to other records

H4

H3

H2 Conclusions

¾ High-resolution MIS 3 record ¾ Lake Manix very sensitive to climate/runoff ¾ Broad features of record (but not all details) most similar to far southwest lakes: Babicora, Baldwin ¾ MIS-3 lake levels correspond to SOME events in marine / ice records: ¾ Low levels during H4 and H3; H2 occurred during cutting of Afton Canyon ¾ Some high levels match D-O (warm) events—but major highstands at ~30 and 25 ka do not Helpful ideas will be appreciated!